Method and apparatus for electron density measurement and verifying process status

ABSTRACT

An equipment status monitoring system and method of operating thereof is described. The equipment status monitoring system includes at least one microwave mirror in a plasma processing chamber forming a multi-modal resonator. A power source is coupled to a mirror and configured to produce an excitation signal extending along an axis generally perpendicular to a substrate. A detector is coupled to a mirror and configured to measure an excitation signal. A control system is connected to the detector that compares a measured excitation signal to a normal excitation signal in order to determine a status of the material processing equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. application Ser. No.60/352,502, filed on Jan. 31, 2002, the entire contents of which areherein incorporated by reference. The present application is related toco-pending International Application No. PCT/US00/19539, Publication No.WO 01/06402, published on Jan. 25, 2001; International Application No.PCT/US00119536, Publication No. WO 01/06544, published on Jan. 25, 2001;International Application No. PCT/US00/19535, Publication No. WO01/06268, published on Jan. 25, 2001; International Application No.PCT/JUS00/19540, Publication No. WO 01/37306, published on May 25, 2001;U.S. Application No. 60/330,518, entitled “Method and apparatus for wallfilm monitoring”, filed on Oct. 24, 2001; U.S. Application No.60/330,555, entitled “Method and apparatus for electron densitymeasurement”, filed on Oct. 24, 2001; co-pending U.S. Application No.60/352,504, entitled “Method and apparatus for monitoring and verifyingequipment status,” filed on Jan. 31, 2002; co-pending U.S. ApplicationNo. 60/352,546, entitled “Method and apparatus for determination andcontrol of plasma state,” filed on Jan. 31, 2002; and co-pending U.S.Application No. 60/352,503, entitled “Apparatus and method for improvingmicrowave coupling to a resonant cavity,” filed on Jan. 31, 2002. Thecontents of these applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to fabrication of integratedcircuits in the semiconductor industry.

2. Discussion of the Background

The fabrication of integrated circuits (IC) in the semiconductorindustry typically employs plasma to create and assist surface chemistrywithin a plasma processing chamber necessary to remove material from anddeposit material to a substrate. In general, plasma is formed within theprocessing chamber under vacuum conditions by heating electrons toenergies sufficient to sustain ionizing collisions with a suppliedprocess gas. Moreover, the heated electrons can have energy sufficientto sustain dissociative collisions and, therefore, a specific set ofgases under predetermined conditions (e.g., chamber pressure, gas flowrate, etc.) are chosen to produce a population of charged species andchemically reactive species suitable to the particular process beingperformed within the chamber (e.g., etching processes where materialsare removed from the substrate or deposition processes where materialsare added to the substrate).

The semiconductor industry is constantly striving to produce smaller ICsand to increase the yield of viable ICs. Accordingly, the materialprocessing equipment used to process the ICs have been required to meetincreasingly more stringent performance requirements for etching anddeposition processes (e.g., rate, selectivity, critical dimension,etc.).

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for monitoringequipment status in a material processing chamber. The present inventionadvantageously provides a method and apparatus that enables devicemanufacturers to satisfy more stringent performance requirements formaterial processing equipment used in the semiconductor industry.

The present invention advantageously provides an equipment statusmonitoring system for a material processing system. The equipment statusmonitoring system of the present invention includes at least onemulti-modal resonator. The invention further includes a power sourcecoupled to the at least one multi-modal resonator, wherein the powersource is configured to produce an excitation signal extending along anaxis generally perpendicular to a substrate. Additionally, a detector iscoupled to the at least one multi-modal resonator, wherein the detectoris configured to measure the excitation signal. The invention alsoincludes a control system connected to the detector and configured toprovide a comparison of the measured excitation signal with a normalexcitation signal corresponding to a normal status, wherein thecomparison facilitates the determination of an equipment status.

The present invention further advantageously provides a method ofmonitoring a status of a material processing system. The materialprocessing system includes a chamber, at least one multi-modal resonatorpositioned in relation to the chamber, a power source coupled to the atleast one multi-modal resonator to produce an excitation signalextending along an axis generally perpendicular to a substrate, and adetector coupled to the at least one multi-modal resonator. The methodof the present invention includes the steps of sweeping an outputfrequency of the power source in order to produce the excitation signal,recording the excitation signal using the detector, comparing theexcitation signal to a normal excitation signal, and determining thestatus of the material processing system from the comparison of themeasured excitation signal and the normal excitation signal.

The present invention further advantageously provides a method ofaltering the status of the material processing system by adjusting atleast one of a chamber condition and a process recipe.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of an electron density measurement system fora plasma processing chamber according to an embodiment of the presentinvention;

FIG. 2 is a schematic view of an electron density measurement system fora plasma processing chamber according to an embodiment of the presentinvention;

FIG. 3 is an enlarged, exploded, cross-sectional view of a microwavemirror having an aperture, a microwave window and associated mountingstructure;

FIG. 4 is a graphical representation of an exemplary cavity transmissionfunction showing several longitudinal resonances and a respective freespectral range;

FIG. 5 is a flow diagram of a method of monitoring electron density in aplasma processing chamber according to an embodiment of the presentinvention;

FIG. 6 is a schematic view of a multi-site electron density measurementsystem for a plasma processing chamber according to an alternativeembodiment of the present invention;

FIG. 7 is a schematic view of a multi-site electron density measurementsystem for a plasma processing chamber according to an alternativeembodiment of the present invention;

FIG. 8 is a flow diagram of a method of monitoring electron density atmultiple sites in a plasma processing chamber according to an embodimentof the present invention;

FIG. 9 is a top view of a non-linear mirror configuration for use in amulti-side measurement system according to one embodiment of the presentinvention;

FIG. 10 is a schematic view of an equipment status monitoring system fora material processing chamber according to an embodiment of the presentinvention;

FIG. 11 is a flow diagram of a method of monitoring equipment status ina material processing chamber according to an embodiment of the presentinvention; and

FIG. 12 is a flow diagram of a method of monitoring equipment status ina material processing chamber according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF TlE PREFERRED EMBODIMENTS

The present invention generally relates to fabrication of integratedcircuits in the semiconductor industry. The present inventionadvantageously provides a method and apparatus that enablessemiconductor manufacturers to satisfy more stringent performancerequirements for material processing equipment used in the semiconductorindustry.

A method of improving the performance of material processing equipmentis to monitor and control plasma electron density within the processingchamber during the manufacturing process. Ideally, the plasma electrondensity is maintained such that the processes being performed areuniformly acting upon the entire surface of the substrate upon whichwork is being performed.

An exemplary device used to measure plasma electron density is amicrowave system of suitably high frequency to exceed the electronplasma frequency. The device includes at least one reflecting surfaceimmersed in the plasma. Microwave power is coupled to a multi-modalresonator (e.g. open resonant cavity) and a detector is utilized tomonitor the transmission of microwave power through the multi-modalresonator. For a Gaussian beam, cavity transmission occurs at discretefrequencies, and the discrete frequencies correspond to an integernumber of half wavelengths between the apex of each mirror, as expressedby the following equation: $\begin{matrix}{{v_{m,n,q} = {v_{0,0,q} = {\frac{c}{2\eta\quad d}\left( {q + \frac{1}{2}} \right)}}},} & (1)\end{matrix}$where ν_(0,0,q) is a resonant frequency of mode order q (assuming onlylongitudinal modes, i.e. m=n=0), c is the speed of light in a vacuum, ηis the index of refraction for the medium bounded by the mirrors and dis the mirror spacing (apex-to-apex) for the multi-modal resonator. Fora vacuum, η=1, however, the presence of plasma or, more specifically, apopulation of free electrons leads to a reduction of the index ofrefraction or an observable increase (shift) of the cavity resonancefrequencies ν_(0,0,q). For a given mode q, the shift in frequency can berelated to the index of refraction n and, thereafter, the (integrated)electron density <n_(e)>, is expressed by the following equation:$\begin{matrix}{{\left\langle n_{e} \right\rangle \cong {\frac{8\pi^{2}ɛ_{o}}{e^{2}}v_{o}\Delta\quad v}},} & (2)\end{matrix}$for ν₀>ω_(pe)/2π. For further details, the use of the above system tomeasure plasma electron density is described in International App. No.PCT/US00/19539 (based upon U.S. Ser. No. 60/144,880), International App.No. PCT/US00/19536 (based upon U.S. Ser. No. 60/144,883), InternationalApp. No. PCT/US00/19535 (based upon U.S. Ser. No. 60/144,878), andInternational App. No. PCT/US00/19540 (based upon U.S. Ser. No.60/166,418), each of which is incorporated herein by reference in theirentirety.

An apparatus is now described that enables real-time spatial resolutionof the electron density. In an embodiment depicted in FIG. 1, amonitoring system 130 is aligned substantially perpendicular to thewafer plane 129 wherein a first reflecting surface is immersed in theplasma within an upper wall opposite a second reflecting surface. Themonitoring system 130 can be, for example, a multi-modal resonator. Thefirst reflecting surface can be, for example, a microwave mirror 140 andthe second reflecting surface can be, for example, a substrate 114and/or substrate holder 128.

An embodiment of a plasma processing system 110 as depicted in FIG. 1includes a plasma chamber 120 and a monitoring system 130 for use in theplasma chamber 120. The monitoring system 130 generally includes amicrowave mirror 140, a power source 160, a detector 170, and a controlsystem 180. The plasma chamber 120 generally includes a base wall 122,an upper wall 124, and side-walls including a first side wall 126 and asecond side wall 127. The plasma chamber 120 also includes a substrateholder (or chuck assembly) 128 having a wafer plane 129, such as anupper surface of the substrate holder 128 upon which a substrate 114 ispositioned in order to be processed within the plasma chamber 120.

The microwave mirror 140 can have, for example, a concave surface 142and is provided within the plasma chamber 120. In the embodimentdepicted in FIG. 1, the mirror 140 is integrated within the upper wall124 of the plasma chamber 120. The concave surface 142 of the microwavemirror 140 is oriented opposite the substrate holder 128.

The power source 160 is coupled to the microwave mirror 140 and isconfigured to produce a microwave signal. The microwave signal ormicrowave beam 145 produced by the power source 160 extends in adirection generally perpendicular to a wafer plane 129 of a substrateholder 128 adapted to be provided within the plasma chamber 120. Theembodiment of the monitoring system 130 depicted in FIG. 1 also includesthe detector 170 coupled to the microwave mirror 140. The detector 170is configured to measure a voltage related to the microwave signalwithin the plasma chamber 120. The control system 180 is connected tothe detector 170 and is configured to measure a first voltage during avacuum condition, measure a second voltage during a plasma condition,and determine an electron density from the difference between the firstand second measured voltages. The control system 180 that includes alock-on circuit 182 connected to the power source 160 and the detector170, and can additionally include a computer connected to the lock-oncircuit 182.

The upper wall 124 of the chamber 120 includes a waveguide aperture 144configured to couple the power source 160 to the microwave mirror 140,and a detector aperture 146 configured to couple the detector 170 to themicrowave mirror 140. Microwave window assemblies 190 each including amicrowave window 192 are provided for both the waveguide aperture 144and the detector aperture 146. The microwave window assemblies 190 canbe implemented like the microwave window assembly depicted in FIG. 3 tobe described below. The microwave windows are implemented to maintainvacuum integrity. Alternately, separate mirrors can be provided for thepower source 160 and the detector 170.

In an alternate embodiment as depicted in FIG. 2, the upper wall 224 ofprocess chamber 120 can comprise an inner domed surface within which amonitoring system 130 can be formed. In an alternate embodiment, thechamber 120 can be frusto-conical.

FIG. 3 depicts a detailed schematic of a microwave window assembly 190for mirror 140, which is used to provide a coupling from the powersource 160 through aperture 144. A window assembly 190 having anidentical structure is preferably provided for the second aperture 146in mirror 140, which is used to provide a coupling to the detector 170.

The microwave window assembly 190 depicted in FIG. 3 includes amicrowave window 192 that is fastened between a window flange 194 and arear surface 147 of the microwave mirror 140. In the embodiment depictedin FIG. 3, the window 192 is provided within a recessed portion 148 onthe rear surface 147 of microwave mirror 140. The microwave window 192is provided between a first O-ring 196 provided on the window flange 194and a second O-ring 197 provided on the rear surface 147 of microwavemirror 140. A plurality of fasteners 198 are provided to mechanicallyconnect the window flange 194 to microwave mirror 140 such that themicrowave window 192 is securely mounted to the rear surface 147 ofmicrowave mirror 140. The window 192 is centered on a waveguide aperture195 extending through the window flange 194 and the waveguide aperture144 extending through microwave mirror 140. The rectangular waveguideapertures 144 and 195 are sized for a specific microwave band ofoperation and are fabricated using Electrical Discharge Machining (EDM).The microwave window 192 is fabricated from a dielectric material suchas alumina, sapphire, aluminum nitride, quartz, polytetrafluoroethylene(PTFE/Teflon), or Kapton. The window 192 is preferably fabricated fromsapphire due to its compatibility with the oxide etch processes.

The microwave mirror 140 is preferably fabricated from aluminum. Inalternative embodiments, the microwave mirror 140 is anodized withpreferably a 10 to 50 micron thick anodization or coated with a materialsuch as Yttria (Y₂O₃).

The microwave power source 160 is preferably an electronically tunablevoltage controlled Gunn diode oscillator (VCO). When the VCO is biasedwith a direct current voltage, the output frequency can be varied oversome spectral range. Therefore, the VCO specifications generally includecenter frequency, bandwidth and minimum output power. In order tofacilitate the use of the above-described system, it is preferred thatthe VCO bandwidth is at least comparable to the free spectral range(FSR). For example, at 35 GHz, a commercially available VCO is aWBV-28-20160RI Gunn diode oscillator offered by Millitech, LLC (20Industrial Drive East, South Deerfield, Mass. 01373-0109). Thespecifications for this VCO include a center frequency of 35 GHz withplus or minus 1 GHz bandwidth and a minimum output power of 40 mW. A 2GHz bandwidth can be suitable for a spacing (between the upper wall 20and wafer 35) of approximately 7.5 cm. The bias tuning range cangenerally extend from ±25 V to −25 V, thereby adjusting this biasvoltage leads to a change in the output frequency of the VCO. Inalternate embodiments, operation at higher frequencies, such as 70 GHzand 105 GHZ, can be achieved using a frequency doubler (MUD-15-6F00) ortripler (MUT-10-16F00) with the above mentioned VCO. Using the aboveconfiguration, a center frequency of 70 GHz with plus or minus 2 GHzbandwidth and a minimum output power of 0.4 to 0.9 mW and a centerfrequency of 105 GHz with plus or minus 3 GHz bandwidth and a minimumoutput power of 0.4 to 0.7 mW can be achieved, respectively. In anadditional embodiment, a 94 GHz VCO (Model GV-10) is used and iscommercially available from Farran Technology LTD (Ballincollig, Cork,Ireland). The Model GV-10 VCO has a center frequency of 94 GHz with plusor minus 750 MHz bandwidth, a minimum output power of 10 mW, and avaractor tuning range of 0 to −25 V. For small mirror spacing (i.e. <5cm), a microwave input with sufficient power and large bandwidth couldbe required. In one embodiment, an active multiplier chain is utilizedwith a low frequency microwave oscillator to achieve bandwidths as greatas plus or minus 12 GHz. For example, an active multiplier chain for usein the range of 75 to 100 GHz is a Model AMC-10-R000 that iscommercially available from Millitech, LLC. In general, the power shouldbe sufficiently high to achieve a usable signal-to-noise ratio for thediagnostic, however, the power should not be increased above tens ofmilliwatts in order to avoid wafer damage.

The detector 170 is preferably a general purpose diode detector such asthose commercially available from Millitech, LLC. For example, aDXP-15-RNFW0 and a DXP-10-RNFW0 are general purpose detectors in theV-band (50 to 75 GHz) and W-band (75 to 110 GHz), respectively. Thedetector detects an excitation signal representing (either linearly ornon-linearly) the microwave power transmitted through the multi-modelresonator.

The embodiment of the present invention depicted in FIG. 1 has a controlsystem 180 that includes a lock-on circuit 182 connected to the powersource 160 and the detector 170, and a computer 184 connected to thelock-on circuit 182. The lock-on circuit 182 can be utilized to lock thefrequency of the microwave signal output from the microwave power source160 to a pre-selected cavity resonance. The lock-on circuit 182superimposes a dither signal (e.g. 1 kHz, 10 mV amplitude square wave)on a direct current voltage substantially near the voltage and relatedoutput VCO frequency that corresponds with a pre-selected longitudinalfrequency in the monitoring system 130 of FIG. 1 (i.e. when the outputfrequency falls within the resonance envelope, an error signal can beproduced to move the output frequency of the VCO to the frequencyassociated with the resonance peak). The signal detected by the detector170 is provided to the lock-on circuit 182, where it represents a firstderivative of the cavity transmission function (transmitted power versusfrequency). The signal input to the lock-on circuit 182 from thedetector 170 provides an error signal by which the direct currentcomponent of the VCO bias voltage is adjusted to drive the VCO outputfrequency to the frequency associated with the peak of a pre-selectedlongitudinal resonance as shown in FIG. 4. FIG. 4 presents an exemplarycavity transmission function (from a negative polarity detector)indicating several longitudinal resonances and the respective freespectral range (FSR). The cavity transmission as shown in FIG. 4 can beobtained by sweeping the VCO across a suitable frequency rangesufficiently greater than the FSR.

As described above, the introduction of plasma within the chamber 120causes a shift in frequency for each of the resonances shown in FIG. 4(i.e. each of the resonances shift to the right in FIG. 4 when theelectron density is increased or the index of refraction is decreasedaccording to equation (1)). Therefore, once the output frequency of theVCO is locked to a selected cavity resonance, the direct current biasvoltage with and without plasma can be recorded and the frequency shiftof the selected resonance is determined from the voltage difference andthe respective VCO calibration. For example, in wafer processing, thedirect current bias voltage is recorded once a new wafer is received bythe process tool for materials processing and prior to the ignition ofplasma. Hereinafter, this measurement will be referred to as the vacuumresonance voltage. Once the plasma is formed, the direct current biasvoltage is obtained as a function of time for the given wafer and thetime varying voltage difference or ultimately electron density (viaequation (2)) is recorded.

FIG. 5 is a flowchart of a method of monitoring the bias voltagerepresentative of electron density from wafer-to-wafer utilizing thesystems described in FIGS. 1 and 2. The process begins with a step 200of loading a wafer and preparing the chamber for process conditions(i.e. evacuating the chamber, initiating gas flow, etc.). Once the waferis loaded, a cavity resonance is selected and the lock-on circuit isprogrammed to lock the VCO output frequency to the selected resonantfrequency. The VCO bias voltage corresponding to the pre-selectedresonance during a vacuum condition is measured in step 202 and theprocess proceeds according to a process recipe stored on the processcomputer in step 204. During the process in step 206, a second VCO biasvoltage under a plasma condition is measured as a function of time, adifference between the second VCO bias voltage and the first VCO biasvoltage is computed as a function of time, an electron density isdetermined from the voltage difference per equation (2), and theelectron density is displayed through a graphical user interface (GUI)as a function of time during the process. The measurements of steps 202and 206 can be, for example, a single signal comprising the measuredvoltage as a function of time. When the process is complete, the statusof the batch is evaluated in step 212. If the batch is incomplete, anext wafer is processed in step 208 and steps 200 through 212 arerepeated. If the batch is complete in step 212, a subsequent batch canbe processed.

The present invention provides a method of monitoring electron densityin a plasma chamber, such as that depicted in FIGS. 1 and 2. Forexample, the plasma chamber 120 includes a microwave mirror 140 having aconcave surface 142 located opposite a substrate holder 128 within theplasma chamber 120, a power source 160 coupled to the microwave mirror140 and configured to produce a microwave signal extending along an axisgenerally perpendicular to a wafer plane 129 of the substrate holder128, and a detector 170 coupled to the microwave mirror 140. The methodof the present invention includes the steps of loading a wafer 114 inthe plasma chamber 120, setting a frequency of a microwave signal outputfrom the power source 160 to a resonance frequency, and measuring afirst voltage of the microwave signal during a vacuum condition withinthe plasma chamber 120 using the detector 170. The method furtherincludes the steps of processing the wafer 114, measuring a secondvoltage of the microwave signal during a plasma condition within theplasma chamber 120 using the detector 170, and determining an electrondensity (per equation (2)) from a difference between the second measuredvoltage and the first measured voltage.

The configuration described above and depicted in FIGS. 1, 2, 3 and 5enables the measurement of the integrated electron density in amonitoring system 130 within the influence of the microwave beam. Inaddition to monitoring the integrated plasma density at a single regionabove substrate 114, an alternate embodiment can be configured tomonitor the plasma density at more than one location above substrate114. The process uniformity which is strongly affected by the uniformityof the plasma density is critical in achieving maximum yield and qualityof devices across an entire 200 mm to 300 mm wafer (and larger).

In an alternate embodiment as depicted in FIG. 6, a plurality ofmonitoring systems 130 a, 130 b, and 130 c substantially identical tothose described above are employed with respective mirrors 140 a, 140 b,and 140 c to achieve spatially resolved electron density measurements.The plurality of monitoring systems 130 a, 130 b, and 130 c includemicrowave mirrors 140 a, 140 b, and 140 c that are provided in a spatialarray located opposite the substrate holder 128. The monitoring systemsof such an array can be operated by simultaneously using the method ofmonitoring electron density in a plasma chamber as depicted in FIG. 1.In such a configuration, the electron density can be determined atmultiple sites above the substrate 114, and these measurements can be,for example, correlated with the process performance parameters (i.e.spatial distribution of etch rate, etch selectivity, etc.). Themulti-site measurement of electron density can ultimately be employed todiagnose the uniformity of a process.

In the embodiment depicted in FIG. 6, a linear array of mirrors isprovided, however, other configurations of the mirror array can beutilized to provide for an even distribution of monitoring systems abovethe substrate holder 128, as discussed later with respect to FIG. 9.

In an alternate embodiment as depicted in FIG. 7, the upper wall 224 ofprocess chamber 120 can be curved; a plurality of monitoring systems 130a-c can be formed within the curved wall. In an alternate embodiment,the chamber 120 can be frusto-conical.

FIG. 8 is a flowchart of a second method of monitoring the bias voltagerepresentative of electron density from wafer-to-wafer utilizing thesystem described in FIG. 5. The process begins with a step 300 ofloading a wafer and preparing the chamber for process conditions (i.e.evacuating the chamber, initiating gas flow, etc.). Once the wafer isloaded, a cavity resonance is selected and the lock-on circuit isprogrammed to lock the VCO output frequency to the selected resonantfrequency for each multi-modal resonator 130(a-c) in FIGS. 6 and 7. TheVCO bias voltage corresponding to the pre-selected resonance during avacuum condition is measured in step 302 (i.e. for each multi-modalresonator 130 a-c) and the process proceeds according to a processrecipe stored on the process computer in step 304. During the process instep 306, a second VCO bias voltage under a plasma condition is measuredas a function of time, a difference between the second VCO bias voltageand the first VCO bias voltage is computed as a function of time, anelectron density is determined from the voltage difference per equation(2), and the electron density is displayed through a graphical userinterface (GUI) as a function of time during the process. Step 306 isrepeated for each multi-modal resonator (130 a-c) in FIGS. 6 and 7. Themeasurements of steps 302 and 306 can be, for example, a single signalcomprising the measured voltage as a function of time. At the completionof processing for a given wafer, the uniformity of the electron densityis computed and a determination of whether the uniformity is withinprescribed limits is made in step 314. If the uniformity of electrondensity exceeds the prescribed limit, then an operator is notified instep 320. When the process is complete, the status of the batch isevaluated in step 312. If the batch is incomplete, a next wafer isprocessed in step 308 and steps 300 through 314 are repeated. If thebatch is complete in step 312, a subsequent batch can be processed instep 316.

FIG. 9 is a top view of a multi-side monitoring system. While an arrayof seven sites is shown, more or fewer sites can be used. The array canbe non-linear (as shown in FIG. 9) or linear (as shown in FIGS. 6 and7). The spacing between sites can be uniform or non-uniform and may varywith radius.

As an alternative to the processes depicted in FIGS. 5 and 8, theprocessing of a batch can be terminated mid-batch if the uniformity isnot within prescribed limits. In such an embodiment, the system trackswhich wafers still need to be processed when the wafer cartridge isreloaded.

Returing again to FIG. 4, the frequency spectrum of the cavitytransmission is strongly dependent on several properties of thesurrounding structures that are in substantial contact with themulti-modal resonator. These properties can include, but are not limitedto, diagnostic properties such as, for example, the mirror alignment,size and design; chamber assembly properties such as, for example, theproximity of the chamber structure surrounding the multi-modal resonatorand the materials comprising these structures; properties of thesubstrate such as, for example, the substrate material, thickness andsize, and the substrate proximity to the multi-modal resonator; andproperties of consumable elements such as size, material and proximityto the multi-modal resonator.

Due to the finite size of the multi-modal resonator, i.e. the diameterof the mirror 140, and the diameter of the related microwave beam thatextends between the mirror and substrate, electromagnetic energy“spills” from the periphery of the mirror and interacts with thesurrounding structure. Some of this energy is dissipated in thestructure and, hence, it is lost to heat; however, some of this energyis scattered from the surrounding structure and re-enters themulti-modal resonator. The scattering of electromagnetic energy by thesurrounding structure is very sensitive to the structure geometry, thematerial type and the proximity of the surrounding structure to themulti-modal resonator. Therefore, it is expected that any change to anabove identified property of the surrounding structure can lead to anobservable change in the frequency spectrum of cavity resonances;hereinafter referred to as the resonance spectrum (FIG. 4). As describedabove, a resonance spectrum is one example of an excitation signalproduced by sweeping the power source 160.

During processing, i.e. wafer-to-wafer and batch-to-batch, each of theabove identified properties is subject to change except for theproperties of the diagnostic, which are specifically chosen to beconstant. A diagnostic calibration is typically required at eachinstallation, to be discussed below. Several exemplary cases are nowdescribed, which will lead in to the description of a method ofmonitoring an equipment status according to the present invention. Bycomparing an excitation signal with a normal excitation signal, a changein at least one of a substrate presence, substrate type, substratelocation, chamber assembly status and a consumable status can beidentified.

Improper assembly of the chamber can lead to a substantive change in theresonance spectrum. For example, if the chamber lid assembly is liftedto replace various components such as the gas injection plate, shieldring, focus ring, etc., an improper alignment, size or assembly of there-installed component can be detected with a substantive change in theintegrated resonance spectrum, for instance, zeroth or first moment(mean or variance), viz. I₀ = ∫_(f₁)^(f₂)V_(d)(f)  𝕕f orI₁ = ∫_(f₁)^(f₂)V_(d)²(f)  𝕕f,where V_(d) is the detector voltage as a function of frequency f.Alternatively, a modal amplitude for a given resonance can be monitored,or net change in modal amplitudes can be monitored.

Improper substrate location can also lead to a substantive change in theresonance spectrum. Frequently, the substrate holder or chuck istranslatable within the processing environment and, therefore, capableof vertical movement between a substrate load/unload position and aprocess position. The substrate load/unload position is generallyunchanged; however, the process position can be variable depending uponthe process recipe. The proximity of the chuck to the multi-modalresonator has a distinct effect on the resonance spectrum. In general,the free spectral range (FSR), for the geometry of FIG. 1, changesinversely with the chuck position (i.e., FSR is proportional to 1/d,where d is the spacing between the mirror apex and the upper surface ofthe chuck). Moreover, as the chuck position is changed, the ratio ofmodal amplitudes in a given, measured resonance spectrum can changedepending on the chuck position relative to the multi-modal resonator.Alternatively, a modal amplitude for a given resonance can be monitored,or an n^(th) moment of the resonance spectrum can be monitored. Forexample, Table I presents the free spectral range as a function of theelectrode spacing h (or chuck location). For example, the spacing h canbe the distance between substrate 114 and upper wall 124 in FIG. 10.

Table I: Effect of chuck location on free spectral range (FSR).

Referring to Table I, the free spectral range increases for h=150 mm toh=35 mm (see FIG. 4 for an example of a longitudinal resonance and theFSR).

The presence of the substrate as well as other properties such as, forexample, the substrate thickness, can be detected due to differences inthe observed resonance spectrum with and without a substrate. Ingeneral, the presence of a substrate and, more particularly, a siliconsubstrate leads to a reduction of the modal amplitudes as well as themodal quality factors. The reduction in amplitude can be as great as 10to 80% (depending upon the substrate material, size and thickness).Therefore, the presence of a substrate can be determined by monitoringat least one modal amplitude. Alternatively, the net change in modalamplitudes of an observed resonance spectrum can be monitored.

Substantial erosion of consumable elements can be detected during theirlifetime due to their net effect on the resonance spectrum and, in time,produce a variation of the consumable status. For example, in oxide etchapplications, the material processing chamber is generally clad withseveral consumable elements, such as a silicon gas injection electrode500, quartz shield rings 510, 520 and a silicon focus ring 530 (see FIG.10). During substrate processing, these consumable elements erode and,in time, the resonance spectrum can substantially change indicating apoint to replace the consumable elements. For example, erosion of thesilicon comprising consumable elements can lead to less loss and,therefore, an increase in modal amplitudes or an n^(th) moment of theresonance spectrum, or an increase in a given modal quality factor.Conversely, erosion of the quartz comprising consumable elements canlead to substantive changes in a given, observed resonance spectrum,such as, for example, changes in the ratio of one modal amplitude toanother.

Following the trends above, a variation in equipment status as governedby a substrate presence, substrate type, substrate location, chamberassembly status and a consumable status can be detected by comparing ameasured excitation signal with a normal excitation signal. In oneembodiment, a difference can be detected by comparing at least one modalamplitude. In an alternate embodiment, a difference can be detected byat least one of: a change in a modal amplitude; a net change in themodal amplitudes of a resonance spectrum; a change (including shift) inat least one resonance location(s) (frequency/frequencies) (including ashift in all measured resonance locations); a change in relativespacings between modes (i.e. FSR); a net change in the each of theresonance frequencies; a change in the ratio of one modal amplitude to asecond modal amplitude; a change in a (modal) signal quality factor; achange in an integrated property of the excitation signal such as, forexample, a zeroth moment, a first moment, a second moment and a thirdmoment; and a change in a differentiated property of the excitationsignal such as, for example a slope (first derivative), secondderivative, and third derivative. One such change is the change inresonance location (frequency) (e.g., due to buildup of a film or filmson the resonator mirror(s) or a temperature effect on the stability ofthe VCO).

As mentioned above, the diagnostic generally comprises a specific designand, therefore, once the diagnostic is installed within a processingsystem, the properties of the diagnostic, i.e. size, alignment, etc.,are not susceptible to change. At each installation of the diagnostic,either reinstallation, diagnostic upgrade, diagnostic repair, etc., thematerial processing system, to which it is installed, must becharacterized. Therein, the resonance spectrum (or excitation signal) isrecorded for each process to be performed in the material processingsystem, and a series of normal excitation signals are determined. Forexample, a substrate of given type, material and size, is loaded.Thereafter, the excitation signal is recorded for the system when thesubstrate is located at the load/unload position and the processposition (as specified by the process recipe). These two normalexcitation signals indicate a normal status for substrateloading/unloading and substrate processing, respectively. Moreover, thesubstrate can be removed and the above measurements repeated. Followingthis procedure, a normal substrate presence, a normal substrate type, anormal substrate location, a normal chamber assembly status and a normalconsumable status can be determined and recorded within control system80. For example, Table I will be used below to represent the normalsubstrate location for recipes at different electrode spacings. Once thenormal excitation signals corresponding to the normal excitationstatuses are determined, a method of monitoring the equipment status canbe described.

FIG. 11 is a flowchart 1200 of a method of monitoring the equipmentstatus by measuring an excitation signal. The process begins with step1210, wherein the varactor bias voltage for the power source 60 is sweptaccording to either a periodic (i.e. saw-tooth) or aperiodic function intime. In step 1220, the excitation signal detected by detector 70 isrecorded by control system 80. For example, the detector may record thatthe FSR=3.75 GHz when the process recipe calls for a 40 mm electrodespacing. In step 1230, the measured excitation signal is compared to anormal excitation signal and, depending on the nature of the differencesas described above (if any), the equipment status is determined relativeto the normal status in step 1240. Thus, in the continuing example, themethod would determine that the values for FSR are more similar to a 45mm spacing than a 40 mm spacing, representing a misplacement of thechuck. Using the equipment status, step 1250 proceeds to perform adecision on whether to notify the system operator in step 1260. In thecontinuing example, the operator is notified of the misplacement of thechuck and given the opportunity to tell the system to correct the error.Step 1270 proceeds to perform a decision on whether to alter theequipment status in step 1280. In step 1280, at least one of a substratepresence, a substrate type, a substrate location, a chamber assemblystatus, and a consumable status is adjusted. For example, if requestedby the operator, the chuck would be moved from the incorrect 45 mmspacing to the recipe-specific 40 mm spacing.

A substrate presence can be altered, for example, by loading asubstrate; a substrate type can be altered, for example, by replacingthe current substrate with a substrate comprising a different materialor of a different size; a substrate location can be altered, forexample, by verifying the current chuck position and translating thechuck to a different position; a chamber assembly status can be altered,for example, by verifying proper chamber assembly and performingnecessary corrective action; and a consumable status can be altered, forexample, by replacing at least one consumable element.

FIG. 12 is a flowchart 1300 of a method of monitoring the equipmentstatus by measuring a plurality of excitation signals. The processbegins with step 1310, wherein the varactor bias voltage for the one ormore power sources 160 is swept according to either a periodic (i.e.saw-tooth) or aperiodic function in time. In step 1320, the excitationsignals detected by the detectors 170 in multi-modal resonators 130(a-c)are measured by control system 180. In step 1330, at least one of a sum,difference, multiplication and division of the measured excitationsignals is compared to at least one of a sum, difference, multiplicationand division of the normal excitation signals corresponding to a normalstatus and, depending on the nature of the differences as describedabove (if any), the equipment status is determined relative to thenormal status in step 1340. Using the equipment status, step 1350proceeds to perform a decision on whether to notify the system operatorin step 1360, and step 1370 proceeds to perform a decision on whether toalter the equipment status in step 1380. In step 1380, at least one of asubstrate presence, a substrate type, a substrate location, a chamberassembly status, and a consumable status is adjusted.

It should be noted that the exemplary embodiments depicted and describedherein set forth the preferred embodiments of the present invention, andare not meant to limit the scope of the claims hereto in any way.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. An equipment status monitoring systemcomprising: a plasma chamber; atleast one multi-modal resonator, wherein said multi-modal resonatorcomprises a first reflecting surface, said first reflecting surfacearranged opposite a second reflecting surface, wherein one of said firstand second reflecting surfaces are adapted to be provided within saidplasma chamber; a power source coupled to at least one of said firstreflecting surface and second reflecting surface of said at least onemulti-modal resonator, said power source being configured to produce anexcitation signal extending along an axis generally perpendicular to asubstrate; a detector coupled to said at least one multi-modalresonator, said detector being configured to measure said excitationsignal; and a control system connected to said detector and configuredto provide a comparison of at least one measured excitation signal witha normal excitation signal corresponding to a normal status, whereinsaid comparison determines an equipment status.
 2. The equipment statusmonitoring system according to claim 1, wherein said equipment statusincludes at least one of substrate presence, substrate type, substratelocation, chamber assembly status, and consumable status.
 3. Theequipment status monitoring system according to claim 1, wherein saidnormal excitation signal comprises an excitation signal associated withat least one of normal substrate presence, normal substrate type, normalsubstrate location, normal chamber assembly status, and normalconsumable status.
 4. The equipment status monitoring system accordingto claim 1, wherein said excitation signal is one of a voltage, currentand power representing a microwave power transmitted through saidmulti-modal resonator.
 5. The equipment status monitoring systemaccording to claim 1, wherein said excitation signal is a spectrumcomprising at least one modal frequency.
 6. The equipment statusmonitoring system according to claim 1, wherein said comparison of atleast one measured excitation signal with a normal excitation signalcomprises a comparison of signal amplitude.
 7. The equipment statusmonitoring system according to claim 6, wherein said comparison ofsignal amplitude comprises comparing at least one modal amplitude insaid at least one measured excitation signal to at least one modalamplitude in said normal excitation signal.
 8. The equipment statusmonitoring system according to claim 6, wherein said comparison ofsignal amplitude comprises comparing at least one ratio of a first modalamplitude in said at least one measured excitation signal and a secondmodal amplitude in said at least one measured excitation signal to atleast one ratio of a first modal amplitude in said normal excitationsignal and a second modal amplitude in said normal excitation signal. 9.The equipment status monitoring system according to claim 1, whereinsaid comparison of at least one measured excitation signal with a normalexcitation signal comprises a comparison of at least one of signalfrequency and free spectral range.
 10. The equipment status monitoringsystem according to claim 1, wherein said comparison of at least onemeasured excitation signal with a normal excitation signal comprises acomparison of signal quality factor.
 11. The equipment status monitoringsystem according to claim 10, wherein said signal quality factorcorresponds to a quality factor of at least one resonance mode.
 12. Theequipment status monitoring system according to claim 1, wherein saidcomparison of at least one measured excitation signal with a normalexcitation signal comprises a comparison of an integrated signal. 13.The equipment status monitoring system according to claim 12, whereinsaid comparison of said integrated signal comprises a comparison of atleast one of a zeroth moment, a first moment, a second moment and athird moment of said at least one measured excitation signal and saidnormal excitation signal.
 14. The equipment status monitoring systemaccording to claim 1, wherein said comparison of at least one measuredexcitation signal with a normal excitation signal comprises a comparisonof a differentiated signal.
 15. The equipment status monitoring systemaccording to claim 13, wherein said comparison of a differentiatedsignal comprises a comparison of at least one slope in said at least onemeasured excitation signal with at least one slope in said normalexcitation signal.
 16. A method of monitoring a status of a materialprocessing system, said material processing system including a chamber,at least one multi-modal resonator comprising a first reflectingsurface, said first reflecting surface arranged opposite a secondreflecting surface, wherein one of said first and second reflectingsurfaces are adapted to be provided within said chamber, a power sourcecoupled to said multi-modal resonator, and a detector coupled to saidmulti-modal resonator, said method comprising the steps of: sweeping anoutput frequency of said power source to produce said excitation signalextending along an axis generally perpendicular to a substrate;recording said excitation signal from said multi-modal resonator;comparing said excitation signal with a normal excitation signal,wherein said normal excitation signal corresponds to a normal status ofsaid material processing system; and determining said status of saidmaterial processing system from said comparing.
 17. The method accordingto claim 16, wherein said status of said material processing systemincludes at least one of substrate presence, substrate type, substratelocation, chamber assembly status, and consumable status.
 18. The methodaccording to claim 16, wherein said normal status of said materialprocessing system corresponds to at least one of normal substratepresence, normal substrate type, normal substrate location, normalchamber assembly status, and normal consumable status.
 19. The methodaccording to claim 16, wherein the method further includes altering saidstatus of said material processing system by adjusting at least one ofsaid substrate presence, said substrate type, said substrate location,said chamber assembly status, and said consumable status.
 20. The methodaccording to claim 16, wherein said sweeping said output frequency ofsaid power source comprises varying an input bias voltage of said powersource according to at least one of a periodic and an aperiodicfunction.
 21. The method according to claim 16, wherein said microwavesignal is a voltage proportional to a power transmitted through saidmulti-modal resonator.
 22. The equipment status monitoring systemaccording to claim 16, wherein said excitation signal is a spectrumcomprising at least one modal frequency.
 23. The method according toclaim 16, wherein said comparing said excitation signal with said normalexcitation signal comprises comparing a signal amplitude.
 24. The methodaccording to claim 23, wherein said comparing a signal amplitudecomprises comparing at least one modal amplitude in said excitationsignal to at least one modal amplitude in said normal excitation signal.25. The method according to claim 23, wherein said comparing a signalamplitude comprises comparing at least one ratio of a first modalamplitude in said excitation signal and a second modal amplitude in saidexcitation signal to at least one ratio of a first modal amplitude insaid normal excitation signal and a second modal amplitude in saidnormal excitation signal.
 26. The method according to claim 16, whereinsaid comparing said excitation signal with said normal excitation signalcomprises a comparison of at least one of signal frequency and freespectral range.
 27. The method according to claim 16, wherein saidcomparing said excitation signal with said normal excitation signalcomprises a comparison of signal quality factor.
 28. The methodaccording to claim 27, wherein said signal quality factor corresponds toa quality factor of at least one resonance mode.
 29. The methodaccording to claim 16, wherein said comparing said excitation signalwith said normal excitation signal comprises a comparison of anintegrated signal.
 30. The method according to claim 29, wherein saidcomparison of said integrated signal comprises a comparison of at leastone of a zeroth moment, a first moment, a second moment and a thirdmoment of said excitation signal and said normal excitation signal. 31.An equipment status monitoring system, said equipment status monitoringsystem comprising: a plasma chamber; plural multi-modal resonatorsconfigured to produce excitation signals, wherein each of said pluralmulti-modal resonators comprises a first reflecting surface, said firstreflecting surface arranged opposite a second reflecting surface,wherein at least one of said first and second reflecting surfaces areadapted to be provided within said plasma chamber, a power sourcecoupled to at least one of said plural multi-modal resonators, saidplural multi-modal resonators being configured to produce excitationsignals extending along an axis generally perpendicular to a substrate,a detector coupled to each of said plural multi-modal resonators; and acontrol system connected to each detector and configured to provide ameasurement of said excitation signals corresponding to a normal status.32. An equipment status monitoring system according to claim 31, whereinsaid control system is further configured to provide a measurement ofsaid excitation signals corresponding to a status during processing. 33.An equipment status monitoring system according to claim 32, whereinsaid control system is further configured to provide a comparison ofsaid excitation signals corresponding to said status during process withsaid excitation signals corresponding to said normal status.
 34. Anequipment status monitoring system according to claim 33, wherein saidcomparison comprises a comparison of at least one of a sum, difference,multiplication and division of said excitation signals corresponding tosaid status during processing with at least one of a sum, difference,multiplication and division of said excitation signals corresponding tosaid normal status.
 35. An equipment status monitoring system, saidequipment status monitoring system comprising: plural multi-modalresonators configured to produce excitation signals, wherein each ofsaid plural multi-modal resonators comprises a first reflecting surface,said first reflecting surface arranged opposite a second reflectingsurface, a power source coupled to at least one of said pluralmulti-modal resonators, said plural multi-modal resonators beingconfigured to produce excitation signals extending along an axisgenerally perpendicular to a substrate, a detector coupled to each ofsaid plural multi-modal resonators; and a control system connected toeach detector and configured to provide a measurement of said excitationsignals corresponding to a normal status.
 36. An equipment statusmonitoring system, said equipment status monitoring system comprising:at least one multi-modal resonator, wherein said multi-modal resonatorcomprises a first reflecting surface, said first reflecting surfacearranged opposite a second reflecting surface; a power source coupled toat least one of said first reflecting surface and second reflectingsurface of said at least one multi-modal resonator, said power sourcebeing configured to produce an excitation signal extending along an axisgenerally perpendicular to a substrate; a detector coupled to said atleast one multi-modal resonator, said detector being configured tomeasure said excitation signal; and a control system connected to saiddetector and configured to provide a comparison of at least one measuredexcitation signal with a normal excitation signal corresponding to anormal status, wherein said comparison determines an equipment status.